Diagnostic percutaneous transthoracic needle aspiration biopsy (TNAB) under fluoroscopic or ultrasound guidance was performed in 195 patients with peripheral lung lesions. Final diagnosis was confirmed in 178 cases. These consisted of 150 cases of malignant and 28 cases of non-malignant lung lesions. Most cases of the latter belonged to the infectious group. Sensitivity of TNAB in the diagnosis of malignancy and lung infections were 92.0 per cent and 62.5 per cent respectively. Needles with different sizes were used and the needle number 18G was found to obtain both cytological and histological samples and showed the highest sensitivity. Among cases that TNAB provided both types of samples, histology alone showed higher sensitivity in diagnosis than cytology alone. However, by cytological examination, malignant tumors could be interpreted for definite cell type in more cases than by histology. To reach the highest diagnostic yield, the results of both samples should be combined. We also found that the aspirated samples with solid or semisolid features were more diagnostic than those with other features. Pneumothorax, the most common complication of the TNAB procedure, was found in only 2.0 per cent of our series.